Carbonated soft drinks are well known in the prior art. Carbonated soft drinks account for almost half of the global soft drink market. The growth in their popularity has been accompanied by a significant decline in the consumption of milk and milk-based beverages. Concern at the general dietary intake patterns of many western societies has identified that the high intake levels of carbonated soft drinks may be one of the contributory factors in the overall decline in health status and diseases directly related to dietary intake.
Milk is generally accepted as a highly nutritious substance. In the diet, it is an excellent source of high quality protein, riboflavin (vitamin B2), vitamin B12, calcium and phosphorous, and a good source of vitamin A, thiamine (vitamin B1), niacin and magnesium. Although nutritionally beneficial, milk and milk-based beverages are often considered unappealing. Carbonation provides an opportunity to deliver milk and its nutritional benefits in a more appealing manner, and offer a viable alternative to traditional soft drinks.
Prior art exists for the manufacture of milk, and milk-based beverages that vary in composition from the milk-base only (which may include but is not limited to fat-free, low fat and full fat types) through to standard flavoured milks (which typically include sweetening agents, flavours, stabilising agents, chelating agents, food acids etc), compositionally modified (e.g. protein enhanced, or lactose reduced) products, fortified milk-based beverages (includes the addition of one or more vitamin or mineral compounds) and more recently functional milk-based beverages (i.e. products to which ingredients have been added to deliver a specific health benefit). Formulated milk and milk-based beverages are available in, but not limited to, fresh, pasteurised and extended shelf-life (ESL) formats which require refrigerated storage and have a limited shelf-life of typically less than 1 to 6 weeks, and as UHT beverages with ambient temperature shelf-life of up to 18 months.
Milk and milk-based beverages may be manufactured using either fresh, pasteurised or otherwise thermally treated liquid milk as the base milk source, or they may be manufactured from powdered milk using well established recombining techniques.
The use of ultra-heat treatment (UHT) for the manufacture of ambient stable, long-life milks and milk-based flavoured beverages is well known in the prior art. A typical UHT process for milk-based beverages involves preheating the beverage mix to approximately 80° C., followed by rapid heating in a pressurised (approximately 400 kPa) system to prevent boiling, to approximately 140-150° C. (UHT temperature) for a few seconds. This is followed by rapid cooling.
A number of process and equipment configurations to achieve the UHT temperature requirements for milk-based beverages are also well established in the prior art. Such processes may include but are not limited to:
i. Direct systems in which the heating medium, typically steam, comes into direct contact with the product. Direct systems include steam injection where steam is injected directly into the product, and; steam infusion, where the product is introduced into a steam-filled unit. Added water from the steam is removed in flash cooling systems.                ii. Indirect systems here the heat to achieve UHT sterilisation is transferred from the heating media through a wall or partition of a heat exchanger unit.        
Homogenisation of milk-based UHT beverages may occur either before (non-aseptically) the UHT process in indirect systems or post the UHT process (aseptically) in direct systems. Typically post UHT aseptic 2-stage homogenisation, at approximately 40-50° C., is preferred for milk-based beverages as this process contributes to improvements in the texture (reduction of potential graininess) and physical stability of the beverage products. Further rapid cooling to 20° C. or less then occurs prior to the transfer of the liquid to an aseptic tank, where it is held prior to packing.
Although carbonation is a naturally occurring phenomenon in some fermented beverages and natural mineral water, for the purposes of this invention, carbonation is the considered the deliberate introduction of CO2 gas under pressure to the beverage, or water with which the beverage is prepared.
The solubility of CO2 in water is a function of temperature and pressure. At a standard pressure of 1 atmosphere (Atm.) and a temperature of 15.6° C., water will dissolve a quantity of CO2 equal to its own volume (i.e. 1.86 g of dissolved CO2). This serves as the basis to describe levels of carbonation in carbonated beverages, based on gas volumes. Typically in carbonated soft drinks, different gas volumes are characteristic of different flavours. The more acidic flavours such as colas, lemonades, tonic and soda waters typically have gas volumes between 3.0 and 4.0. The sweeter fruit flavours and those of cream sodas have lower carbonation levels typically in the range of 2.5 to 2.8 gas volume and sparkling mineral waters often less and 2.0 gas volumes (Shachman, M. (2005) In: The Soft Drinks Companion—A Technical Handbook for the Beverage Industry, CRC Press, Boca Raton, Florida, U.S.A.; pp. 167 -177).
Carbonated milk and milk-based beverages are currently being sold on the USA market but may not be known to any great extent elsewhere. Whilst the concept is new to many consumers, patents in this field have existed since 1898. One of the most recent patents was taken out by a U.S.A. company known as Mac Farms that has now developed a wide range of functional carbonated milk drinks targeted toward certain market segments. Another recent patent addresses the combination of UHT treatment and carbonisation of milk products to manufacture shelf-stable carbonated milk products.